An anthracosaur swimming in a Carboniferous bayou

PHELPS, Daniel J., Kentucky Paleontological Society, 365 Cromwell Way, Lexington, KY 40503, edrioasteroid@msn.com, CHESNUT, Donald R. Jr., Kentucky Geological Survey, 228 MMRB, University of Kentucky, Lexington, KY 40506-0107, and STORRS, Glenn W., Geier Collections and Research Center, Cincinnati Museum Center, Cincinnati, OH 45203

A tetrapod trackway from the Peach Orchard Coal Zone of the Four Corners Formation (Westphalian B/C) near Hazard, Kentucky was discovered as a float specimen during a recent prospecting trip. This is the first Middle Pennsylvanian tetrapod trackway found in Kentucky and only the second Carboniferous vertebrate trackway known from the state.

The tracks are impressions into the upper surface of a fine-grained, cross-laminated sandstone penetrated by an upright fragment of Calamites sp. Associated strata in the Hazard section are varied and include sands, silts and shales. Numerous upright stumps, and plentiful plant compression fossils are also preserved at the site in a complex depositional montage that represents a succession of stream overbank deposits in a terrestrial setting.

The tracks indicate five toes on the manus and at least four toes on the pes. Distinct, very sharp and recurved claw marks are present on both manus and pes. The best-preserved manus is 5.3 cm long by 5.1 cm wide, and the pes 6.3 cm long by 6.6 cm wide. Track width is approximately 7.4 cm (manus), 10.1 cm (pes). The digits are not elongate. The entire length of the trackway is 27 cm. There is no evidence for a tail drag. Stride length and pace angulation can not be determined accurately from the preserved block.

The trackmaker was approximately 0.6 m long and is of unknown tetrapod affinity, but preliminary candidates include Anthracosauria, as well as early anapsid and diapsid reptiles. Renewed efforts, now underway, to locate in situ specimens may aid in identification of the tracks and their origin.